Several discoveries have been made to address the need for securing messages between a sender and receiver. One such discovery being the Diffie-Hellman algorithm and the Rivest Shamir Adleman public key crypto system discovered in the mid 1970s. The significance of these discoveries is that they have become standards on which present encryption systems are built.
The Diffie-Hellman algorithm is especially suited to secure real time communications. The Diffie-Hellman algorithm requires the participation of both the sender and receiver. To execute, the two participants choose two numbers which in turn are used in conjunction with secret numbers which are correspondingly secret to each of the two participants to derive a third number which is exchanged between the two participants. The exchanged numbers are then used in a process to encrypt the messages between the two participants and then to decrypt the messages. This method therefore requires the active participation of the recipient in order to send a secure message. As a consequence, the system is best suited for only two participants in the message, and is not suited for multiple participants. Furthermore although the system secures the confidentiality of the message satisfactorily it does not ensure the authenticity of the message or the sender in terms of what is known as a “digital signature”. As such, the Diffie-Hellman algorithm is predominantly used to secure the real time communication sessions between a sender and a receiver over a network.
The Rivest Shamir Adleman (RSA) public key crypto system, while inspired by the Diffie-Helman algorithm, developed, a method that 1.) does not require the active participation of the recipient, 2.) allows for more than two participants in a message, and 3.) established a framework to provide authenticity of both the sender and of the message itself in addition to securing the message between the sender and the recipient(s).
Securing messages between senders and recipients can be accomplished in an infinite number of ways. To secure email, arguably the most widely deployed application on the Internet, the S/MIME standard was developed in the late 1990s. While there are proprietary methods for securing email messages such as those developed by organizations such as PGP, Hushmail, Zixit, Ziplip etc., S/MIME has become the dominant world standard to secure email communications.
The S/MIME protocol was established by RSA Data Security and other software vendors in 1995. The goal of S/MIME was to provide message integrity, authentication, non-repudiation and privacy of email messages through the use of Public Key Infrastructure (“PKI”) encryption and digital signature technologies. Email applications that support S/MIME assure that third parties, such as network administrators and ISPs, cannot intercept, read or alter messages. S/MIME functions primarily by building security on top of the common MIME (Multipurpose Internet Mail Extension) protocol, which defines the manner in which an electronic message is organized, as well as the manner in which the electronic message is supported by most email applications.
Currently, the most popular version of S/MIME is V3 (version three), which was introduced in July, 1999. Further information on S/MIME standardization and related documents can be found on the Internet Mail Consortium web site and the IETF S/MIME working group web site.
The S/MIME V3 Standard consists generally of the following protocols:                Cryptographic Message Syntax (RFC 2630);        S/MIME Version 3 Message Specification (RFC 2633); and        S/MIME Version 3 Certificate Handling (RFC 2632).        
S/MIME and similar secure message systems rely on PKC to invoke security. With S/MIME security, a MIME message is secured by digitally signing the message which is conducted by encrypting a message digest hash with the private key of the sender. This is what is known as a digital signature. Optionally, the message content with the digital signature is encrypted using the public key of the recipient. The encrypted message and digital signature comprise the S/MIME email message that is then sent to the recipient. Upon receiving the message, the recipient's private key is used to decrypt the message. The recipient re-computes the message digest hash from the decrypted message and uses the public key of the sender to decrypt the original message digest hash (the digital signature) and compares the two hashes. If the two hashes are the same, the recipient has validation of the authencity of the sender and of the integrity of the message. Consequently, S/MIME and similar secure message systems generally require that both the sender and the recipient(s) be enrolled in a PKC system and that the public keys of each be accessible in order for the message to be secured and for the sender and message to be authenticated. As such, if the recipient is not enrolled in a PKI, or the sender does not have access to the recipient's(s') key(s), the sender will not be able to send a secure message to the recipient(s).
What is needed therefore is a system, computer program and method for delivering encrypted messages to recipient(s) where the sender does not possess the credentials of the recipient(s) or some subset thereof. What is further needed is the aforesaid system, computer program and method that can access or generate message encryption keys, which can be used by the sender to ensure the privacy of the message for the recipient. What is still further needed is the aforesaid system, computer program and method that is easily deployed in either a browser or on a client application provided at the network-connected devices themselves. What is also needed is a web-based or client based system, computer program and method whereby the encryption persists throughout the communication and storage of data. What is also needed is a web-based or client-based system, computer program and method whereby the message decryption key is stored securely and accessed securely by the recipient in order to decrypt the message.